Little Busters! (リトルバスターズ! Ritoru Basutāzu!) is a visual novel with an eroge version called Little Busters! Ecstasy. The visual novel was the first part of the series to be released, several manga adaptations and three seasons of anime following after.

The story revolves around the main protagonist Riki Naoe, a young male high school student. When Riki was a child, his parents died, leaving him hopeless and depressed. A group of three young boys and one girl his age saved him who referred to themselves as the Little Busters, a group dedicated to fighting evil and preserving justice. The leader of the group was Kyousuke Natsume who had a younger sister named Rin. The other two members were Masato Inohara and Kengo Miyazawa, who were rivals despite being friends. They took Riki out and played together with him during his time of need, making him the fifth Little Busters member. In time, Riki enjoyed playing with them, and his grief over his parents gradually faded away. When the story begins, Riki and his friends are seemingly in their second year of high school, except for Kyousuke who is in his third year. They still hang out together, and enjoy their school life.

The story opens on Sunday, May 13, 2007, and the next day at school, Kyousuke decides that the Little Busters are going to play a baseball game, except they do not have enough members to have a complete team. Kyousuke gives Riki and Rin the task of going around school to find more members to join, preferably girls so as not to leave Rin the lone girl. Riki finds five girls his age willing to help him out. They are: Komari Kamikita, a childish girl who is very clumsy; Haruka Saigusa, a problem child who likes to start uproars for her own enjoyment; Kudryavka Noumi, a one-quarter Japanese girl in the home economics club who is very bad in English; Yuiko Kurugaya, a girl who is given respect from her peers, and has a self-sufficient personality; and Mio Nishizono, a calm girl with a weak body who is always seen holding a parasol when outside. Throughout the game, Riki hangs out with these girls and learns more about them.

The story's main part takes place in what seems to be a normal high school, but in fact all took place in the school term previous to Little Busters!, and Riki and Rin are reliving it in an artificial world created by Kyousuke. They, and the other main characters, were involved in a bus accident during a school excursion, and only the two of them will survive. Kyousuke created the artificial world to make them strong enough to deal with what will happen when they awaken in the real world. The world loops, but though they forget what happens, Riki and Rin do grow stronger, and Kyousuke hopes that they will eventually be strong enough to leave the world. They do manage to survive and get away from the crash site before Riki collapses due to his chronic illness, narcolepsy. Riki vows to fight against his narcoleptic condition, which was the reason why he was only able to save Rin and merely get away from the explosion before collapsing.

Rejecting this turn of events, Rin travels back into the artificial world again (this time created by Riki and Rin) and helps Riki overcome his weakness, after which the two of them go back to waking up at the crash site. This time, Riki and Rin work together to save everyone at the crash scene. It is revealed that Kyousuke, who sneaked onto the bus (as a third year he was not allowed to go), managed to block the leak hole on the gas tank to delay the explosion, despite his injuries being far greater than anyone else. Riki and Rin barely manage to save everyone on the bus before it explodes, though Riki and Rin were knocked unconcious from the explosion while trying to save Kyousuke. Everyone in the bus recovers from their injuries, although Kyousuke's recovery takes longer due to extensive injuries. Finally, after Kyousuke returns, Kyousuke hires a minibus, and the members of the Little Busters set out for another trip.